The artificial blood vessel is an example of the appliance to be implanted. At present, treatment of, for example, aortic aneurysm is conducted by implanting an artificial blood vessel. In particular, the portion of a blood vessel which has an aneurysm is removed by resection, and an artificial blood vessel is implanted in place of the resected portion and connected to the remaining blood vessel by suturing or the like.
The above-mentioned method of surgically implanting the artificial blood vessel for treatment of aortic aneurysm, however, is highly dangerous. Especially, an emergency operation for treatment of a ruptured aneurysm has a low life-saving rate, and an operation of dissecting aortic aneurysm is difficult to conduct and has a high death rate.
Therefore, in order to treat these diseases without a surgical operation, a method has been developed of introducing a catheter into an appliance such as an artificial blood vessel in a collapsed condition into a human organ such as a blood vessel, and transporting the appliance to a desired position such as an affected or constricted portion thereof, where the appliance is released so as to be expanded and implanted there.
The appliance to be implanted is so constructed that a pair of flexibly foldable and elastic end wire rings are arranged, each of the end wire rings is connected by a tubular cover which is made of a sheet of flexible and tensile material and an intermediate wire ring is arranged between both of the end wire rings and fixedly connected to the above-mentioned tubular cover by suturing or with adhesive.
As a method of collapsing the appliance to be implanted, the following method is adopted in which a plurality of hooking means for a pull string to be passed are formed at every other dividing points each of which equally divides the circumference of the front end wire ring into an even number, the front end wire ring is folded into a wavy shape with the dividing points which are provided with a hooking means for a pull string forming forwardly directed peaks and the dividing points which are not provided with a hooking means for a pull string forming the bottoms of forwardly directed valleys, each of the intermediate wire rings and the rear end wire ring is folded into a wavy shape having the same phase as that of the front end wire ring and the whole artificial blood vessel is inserted into a catheter.
However, since the conventional appliance has an arrangement in which the cover is fixedly attached to the front and rear end wire rings along the circumference thereof, the cover tries to follow the movement of the front and rear end wire rings and forms wrinkles near the front and rear end wire rings when the appliance is folded into a wavy shape. Then the wrinkles gather around the folded portion of the wire rings, thereby to be bulky. This may hinder the appliance from being folded into a small size having an appropriate wavy shape. In addition, if the cover is folded into a small size and making wrinkles, the cover may fail to restore smoothly to the original shape in a target position when released. This may hinder the function of the appliance to be implanted as it is intended to.
In order to solve the above problems there is an appliance to be implanted having an arrangement in which a front and rear end wire rings are fixed to a cover not along all of the outer circumference thereof but at several intermittent points so that the front and rear end wire rings can move freely at a certain degree relative to the cover. The appliance to be implanted of this arrangement, however, might cause blood leakage from an annular gap between the cover and the wire rings, if used inappropriately.
The object of the invention is to solve all of the above-mentioned problems.